Sputum induction [SI] is a technique for obtaining a deep sample of secretions from the lungs in a non-invasive manner for diagnostic purposes from patients who are unable to spontaneously expectorate such material on demand.
The sputum can be examined in a variety of ways, according to the judgment of the clinician, for bacteria, fungi, viruses, parasites, or malignant cells. Alternatively, in recent years, patients undergo an invasive procedure known as fiber optic bronchoscopy in which a thin, flexible tube is guided into the patients lungs allowing for suctioning of material. Bronchoscopy is somewhat uncomfortable, costly, occasionally hazardous, time consuming and usually requires a hospital environment to be accomplished safely.
Sputum induction is a long standing procedure traditionally used to obtain material to confirm the diagnoses of pulmonary tuberculosis, a bacterial infection of the lungs. It is also used to follow, in a serial manner, the effectiveness of therapy for this condition.
The technique of sputum induction essentially comprises having the subject breathe a nebulized mist or aerosol of a liquid which acts as a cough inducing agent, for example hypertonic saline solution. The inhaled saline aerosol or mist humidifies and also irritates the subject's airways, thus promoting and facilitating expectoration of a deep sputum sample.
Sputum induction (SI) has historically been confined to the hospital environment and, more specifically, to institutions with special units for tuberculosis patients. Ordinarily a special space is designated exclusively for sputum induction, since deep coughing can result in the aerosolization of potentially infectious droplet nuclei containing tubercle bacilli, which can be carried by air currents to other areas of a hospital. The prior practice in hospitals has utilized a small room, usually isolated by closing off the outflow ducting of the central air system. In addition, a large exhaust fan is placed in a window of the isolated room to provide for 20 to 30 total room air exchanges per hour. The isolated room has to be located so that contaminated exhaust air will not be pulled into adjacent rooms or building from outside. Ultraviolet light fixtures are placed in the SI room in a manner to sterilize the air and kill aerosolized microorganisms. Even with these precautions, however, it has been estimated that the number of viable organisms released into the air has been reduced by only about 50%. An additional problem has been that of maintaining a comfortable room temperature, since inflowing heated or cooled air is rapidly vented outside.
Sputum induction has, therefore, never gained acceptance as an office procedure due to the cost and inconvenience of dedicating and modifying a separated and isolated space just for SI, and also due to the small but finite hazard of transmission of tuberculosis or other airborne infectious diseases to susceptible persons in the area.
Therapeutic patient enclosures have been known for at least one hundred years. Such patient enclosures are frequently used, for example, to treat patients who must inhale aerosolized medication. Aerosol pentamidine treatment has been administered in this fashion to HIV infected patients to prevent or delay the occurrence of Pneumocystis pneumonia.
Inhaling medication of whatever composition, often induces coughing. Active pulmonary tuberculosis occurs frequently in immunosuppression HIV+ patients. Thus control of sputum droplets exhaled or resulting from coughing in HIV infected patients is well advised to prevent possible spreading of tuberculosis infection. Pentamidine treatment is regularly given to patients in an outpatient setting such as a clinic or doctor's office, to accommodate out patient treatment of HIV patients. Commercial patient enclosures offering protection from contamination of ambient office or clinic air space with tubercle bacilli have been developed. Such enclosures provide for rapid and therefore multiple air exchanges between the patient enclosure interior and the ambient air in the medical office. This rapid exchange is achieved by means of a high volume blower. Infectious particles are trapped within highly efficient air filters. (For instance, a 0.3 micron filter is adequate to entrap most airborne pathogens.)
A problem with patient enclosures which have been used to administer inhaled pentamidine and other drugs is that they are not adapted for sputum induction. SI requires the delivery of a large volume of nebulized mist of externally generated aerosol particles. For instance, an aerosol of hypertonic saline solution has been successfully used for the purpose. Existing commercial enclosures provide some type of small-aperture nozzle mounted to the wall of the chamber. Through such a nozzle a quantity of air with aerosol mist must be generated and delivered to inside the chamber and then to an enclosed patient. The aerosol is thus diffused throughout the chamber, the concentration of the aerosol reaching the patient is relatively low. By providing a frequent change of air within the chamber the aerosol mist is further diluted preventing the patient from receiving a sufficient amount. Alternatively, aerosolized medication may be administered with a small hand held nebulizer held by the patient within the chamber. Available hand held nebulizers are sufficient to aerosolize only small quantities of medication in liquid droplet form. Thus, with either of these methods of supplying the aerosol mist the patient fails to receive a sufficient quantity for SI.
Sputum induction requires that the aerosol mist be provided in a copious and continuous supply to the patient. Accordingly, the patient's air supply must be heavily laden with nebulized aerosol. To be effective for sputum induction the necessary quantity of aerosol is most conveniently generated exterior to the chamber and delivered into the chamber and ultimately directly to the patient through a mouth piece. A significantly large ventilator tubing specially connected for the purpose is required for delivering directly to the patient an adequate copious volume of externally generated aerosal mist for an effective sputum induction procedure.
The central purpose of my invention is to provide means whereby a patient may inhale an air and aerosol agent mixture generated externally of an airtight secure chamber having a controlled negative pressure therein with respect to the ambient atmospheric pressure. In addition, the chamber must be constructed so that substantially all potentially pathogenic airborne particles exhaled or expectorated by the patient while seated within the chamber are entrapped in a disposable air filter mounted at an exhaust port of the closed chamber.
Earlier therapeutic patient enclosures include those such as U.S. Pat. No. 360,733 issued to Hosford. Hosford's device provided a vapor bath for a human patient; however, it did not enclose the patient's head and thus did not control exhaled, airborne infectious particles.
U.S. Pat. No. 3,902,488 issued to Sheppard related to inducing patient hypothermia. Sheppard, too, failed to control escape of infectious airborne particles in his teaching.
U.S. Pat. No. 4,881,542 issued to Schmidt, et al. is directed toward a tubular flexible tracheal sampling probe, and as such teaches invasive pulmonary sampling.
U.S. Pat. No. 4,981,466 to Lumbert is directed to a medical ventilating and venting apparatus and methods in which a catheter tube is used to evacuate lung secretions. Lumbert teaches an invasive medical procedure for obtaining deep lung secretion samples. The present invention, on the other hand, is directed to an entirely noninvasive technique for diagnostic deep pulmonary sampling.
U.S. Pat. No. 426,609 issued to Tucken is directed to a hand-held device to deliver an irritant through a patient mouthpiece. However, there is no provision in the Tucken patent for trapping exhaled infectious particles.
U.S. Pat. No. 310,568 issued to Emery, is directed to a medical vapor generator, but discloses no means for entrapping infectious particles exhaled by a patient.
Viewing together the aforementioned U.S. Patents, none describes an invention such as the present one, which provides for a novel combination of elements for safely inducing sputum induction in potentially or actively infectious patients. With respect to currently commercially available patient enclosures none are known which provide the combination of necessary conditions and structures for conducting safe sputum induction procedures.